The present invention relates to a process for the hydrotreating of fuels with co-production of hydrogen during operation of the process. More particularly the invention relates to a hydrotreating process in which the hydrocarbon fuel contains renewable organic material which generates carbon monoxide during operation of the process. The carbon monoxide is then converted to hydrogen in the recycle loop by a water gas shift stage.
During the refining of oil feeds, hydrotreatment stages are utilized for the removal of impurities such as sulphur and nitrogen. Hydrocarbon feedstocks and in particular heavy hydrocarbons such as oil and diesel usually contain organic sulphur and nitrogen compounds that in subsequent stages represent undesired impurities because of their negative effect on catalyst activity. Additionally, environmental regulations impose a demand on the production of extremely clean transportation fuels with very low sulphur levels, for instance as low as 10 ppm total sulphur in diesel fuels. The sulphur and nitrogen impurities are therefore hydrogenated during hydrotreatment to hydrogen sulphide and ammonia prior to being treated in a subsequent hydroprocessing stage, where depending on the hydrocarbon feedstock used its value may be increased by rearranging the molecules, for instance by hydrocracking.
The hydrogen needed in the hydrotreatment process is normally provided internally in the process by mixing the hydrocarbon fuel with hydrogen-rich recycle gas produced in the process. Additional hydrogen may be supplied from an external source in the form of a make-up gas which can be combined with the hydrogen-rich recycle gas produced in the hydrotreatment process. The make-up hydrogen is used to compensate for the hydrogen consumed during the hydrotreatment. After passing the hydrotreatment stage by contact with one or more fixed beds of e.g. hydrodesulfurisation (HDS) or hydrodenitrogenation (HDN) catalysts, the hydrocarbon feedstock, for instance an oil feed or diesel being depleted from sulphur and nitrogen, is conducted to a hot separator wherefrom an overhead fraction and a bottom fraction is withdrawn. The overhead fraction is then cooled and mixed with water prior to entering a cold separator, where an overhead fraction in the form of a hydrogen-rich gaseous stream is withdrawn. This hydrogen-rich stream is then recycled to the hydrotreatment stage, while the bottoms fraction containing the cleaned fuel is withdrawn and ready for use, for instance as transportation fuel.
US-A-2002/004533 describes a process for the integration of shift reactors and hydrotreaters, in which the hydrogen-rich recycle stream from the hydrotreating process is combined with hydrogen produced from the water gas shift of a synthesis gas produced in a separate process.
U.S. Pat. No. 3,694,344 describes a process in which part of the hydrogen used in the hydrotreatment stage is obtained from a separate process for the production of hydrogen comprising the reforming of natural gas to produce synthesis gas with subsequent water gas shift for further conversion into a hydrogen-rich gas.
U.S. Pat. No. 3,413,214 discloses a process for the hydrogenation of liquid hydrocarbons in which oxygen gas is added to the liquid hydrocarbon in order to induce the generation of a gas product from the hydrotreatment step that contains carbon monoxide. The gas product is subsequently depleted from hydrogen sulphide and then subjected to water gas shift to convert the carbon monoxide in the gas to hydrogen. The resulting hydrogen-rich stream from the water gas shift is recycled to the hydrotreatment stage. The production of this additional hydrogen reduces the requirement of hydrogen from external sources, for instance as make-up hydrogen.